MPLS Working Group M. Bocci
Internet-Draft Alcatel-Lucent
Intended status: Standards Track G. Swallow
Expires: December 26, 2011 Cisco
E. Gray
Ericsson
June 24, 2011
MPLS-TP Identifiersdraft-ietf-mpls-tp-identifiers-06
Abstract
This document specifies an initial set of identifiers to be used in
the Transport Profile of Multiprotocol Label Switching (MPLS-TP).
The MPLS-TP requirements (RFC 5654) require that the elements and
objects in an MPLS-TP environment are able to be configured and
managed without a control plane. In such an environment many
conventions for defining identifiers are possible. This document
defines identifiers for MPLS-TP management and OAM functions suitable
to IP/MPLS conventions.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
(PWE3) architectures to support the capabilities and functionalities
of a packet transport network as defined by the ITU-T.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 26, 2011.
Copyright Notice
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Internet-Draft MPLS-TP Identifiers June 20111. Introduction
This document specifies an initial set of identifiers to be used in
the Transport Profile of Multiprotocol Label Switching (MPLS-TP).
The MPLS-TP requirements (RFC 5654) [7] require that the elements and
objects in an MPLS-TP environment are able to be configured and
managed without a control plane. In such an environment many
conventions for defining identifiers are possible. This document
defines identifiers for MPLS-TP management and OAM functions suitable
to IP/MPLS conventions. The identifiers have been chosen to be
compatible with existing IP, MPLS, GMPLS, and Pseudowire definitions.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
(PWE3) architectures to support the capabilities and functionalities
of a packet transport network as defined by the ITU-T.
1.1. Terminology
AII: Attachment Interface Identifier
ASN: Autonomous System Number
EGP: Exterior Gateway Protocol
FEC: Forwarding Equivalence Class
GMPLS: Generalized Multi-Protocol Label Switching
IGP: Interior Gateway Protocol
LSP: Label Switched Path
LSR: Label Switching Router
MEG: Maintenance Entity Group
MEP: Maintenance Entity Group End Point
MIP: Maintenance Entity Group Intermediate Point
MPLS: Multi-Protocol Label Switching
NNI: Network-to-Network Interface
OAM: Operations, Administration and Maintenance
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P2P: Point to Point
PW: Pseudowire
RSVP: Resource Reservation Protocol
RSVP-TE: RSVP Traffic Engineering
S-PE: Switching Provider Edge
T-PE: Terminating Provider Edge
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
1.3. Notational Conventions
All multiple-word atomic identifiers use underscores (_) between the
words to join the words. Many of the identifiers are composed of a
set of other identifiers. These are expressed by listing the latter
identifiers joined with double-colon, "::", notation.
Where the same identifier type is used multiple times in a
concatenation, they are qualified by a prefix joined to the
identifier by a dash (-). For example A1-Node_ID is the Node_ID of a
node referred to as A1.
The notation does define a preferred ordering of the fields.
Specifically the designation A1 is used to indicate the lower sort
order of a field or set of fields and Z9 is used to indicated the
higher sort order of the same. The sort is either alphanumeric or
numeric depending on the field's definition. Where the sort applies
to a group of fields, those fields are grouped with {...}.
Note, however, that the uniqueness of an identifier does not depend
on the ordering, but rather, upon the uniqueness and scoping of the
fields that compose the identifier. Further the preferred ordering
is not intended to constrain protocol designs by dictating a
particular field sequence (for example see Section 5.2.1) or even
what fields appear in which objects (for example see Section 5.3).
2. Named Entities
In order to configure, operate and manage a transport network based
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on the MPLS Transport Profile, a number of entities require
identification. Identifiers for the following entities are defined
in this document:
* Global_ID
* Node
* Interface
* Tunnel
* LSP
* PW
* MEG
* MEP
* MIP
Note that we have borrowed the term tunnel from RSVP-TE (RFC 3209)
[2] where it is used to describe an entity that provides a logical
association between a source and destination LSR. The tunnel in turn
is instantiated by one or more LSPs, where the additional LSPs are
used for protection or re-grooming of the tunnel.
3. Uniquely Identifying an Operator - the Global_ID
The Global_ID is defined to uniquely identify an operator. RFC 5003
[3] defines a globally unique Attachment Interface Identifier (AII).
That AII is composed of three parts, a Global_ID which uniquely
identifies an operator, a prefix, and finally, an attachment circuit
identifier. We have chosen to use that Global ID for MPLS-TP.
Quoting from RFC 5003, section 3.2, "The global ID can contain the
2-octet or 4-octet value of the operator's Autonomous System Number
(ASN). It is expected that the global ID will be derived from the
globally unique ASN of the autonomous system hosting the PEs
containing the actual AIIs. The presence of a global ID based on the
operator's ASN ensures that the AII will be globally unique."
A Global_ID must be derived from a 4-octet AS number assigned to the
operator. Note that 2-octet AS numbers have been incorporated in the
4-octet by placing the 2-octet AS number, in the low-order octets and
setting the two high-order octets to zero.
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ASN 0 is reserved and cannot be assigned. A Global_ID of zero means
that no Global_ID is specified. Note that a Global_ID of zero is
limited to entities contained within a single operator and MUST NOT
be used across an NNI.
The Global_ID is used solely to provide a globally unique context for
other MPLS-TP identifiers. While the AS Number used in the Global_ID
MUST be one which the operator is entitled to use, the use of the
Global_ID is not related to the use of the ASN in protocols such as
BGP.
4. Node and Interface Identifiers
An LSR requires identification of the node itself and of its
interfaces. An interface is the attachment point to a server
(sub-)layer, e.g., MPLS-TP section or MPLS-TP tunnel.
We call the identifier associated with a node a Node Identifier
(Node_ID). The Node_ID is a unique 32-bit value assigned by the
operator within the scope of a Global_ID. The structure of the
Node_ID is operator specific and is outside the scope of this
document. However, the value zero is reserved and MUST NOT be used.
Where IPv4 addresses are used, it may be convenient to use the Node's
IPv4 loopback address as the Node_ID, however the Node_ID does not
need to have any association with the IPv4 address space used in the
operator's IGP or EGP. Where IPv6 addresses are used exclusively, a
32-bit value unique within the scope of a Global_ID is assigned.
An LSR can support multiple layers (e.g. hierarchical LSPs) and the
Node_ID belongs to the multiple layer context i.e. it is applicable
to all LSPs or PWs that originate on, have a intermediate point on,
or terminate on the node.
In situations where a Node_ID needs to be globally unique, this is
accomplished by prefixing the identifier with the operator's
Global_ID.
Within the context of a particular node, we call the identifier
associated with an interface an Interface Number (IF_Num). The
IF_Num is a 32-bit unsigned integer assigned by the operator and MUST
be unique within the scope of a Node_ID. The IF_Num value 0 has
special meaning (see Section 7.4, MIP Identifiers) and MUST NOT be
used to identify an MPLS-TP interface.
An Interface Identifier (IF_ID) identifies an interface uniquely
within the context of a Global_ID. It is formed by concatenating the
Node_ID with the IF_Num. That is, an IF_ID is a 64-bit identifier
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formed as Node_ID::IF_Num.
This convention was chosen to allow compatibility with GMPLS. The
GMPLS signaling functional description [4] requires interface
identification. GMPLS allows three formats for the Interface_ID.
The third format consists of an IPv4 Address plus a 32-bit unsigned
integer for the specific interface. The format defined for MPLS-TP
is consistent with this format, but uses the Node_ID instead of an
IPv4 Address.
If an IF_ID needs to be globally unique, this is accomplished by
prefixing the identifier with the operator's Global_ID.
The attachment point to an MPLS-TP Tunnel (see Section 5.1) also
needs an interface identifier. Note that MPLS-TP supports
hierarchical tunnels. The attachment point to a MPLS-TP Tunnel at
any (sub-)layer requires a node-unique IF_Num.
5. MPLS-TP Tunnel and LSP Identifiers
In MPLS the actual transport of packets is provided by label switched
paths (LSPs). A transport service may be composed of multiple LSPs.
Further the LSPs providing a service may change over time due to
protection and restoration events. In order to clearly identify the
service we use the term "MPLS-TP Tunnel" or simply "tunnel" for a
service provided by (for example) a working LSP and protected by a
protection LSP. The Tunnel_ID identifies the transport service and
provides a stable binding to the client in the face of changes in the
the data plane LSPs used to provide the service due to protection or
restoration events. This section defines an MPLS-TP Tunnel_ID to
uniquely identify a tunnel, and an MPLS-TP LSP_ID to uniquely
identify an LSP associated with a tunnel.
For the case where multiple LSPs (for example) are used to support a
single service with a common set of end-points, using the Tunnel_ID
allows for a trivial mapping between the server and client layers,
providing a common service identifier which may be either defined by,
or used by, the client.
Note that this usage is not intended to constrain protection schemes,
and may be used to identify any service (protected or unprotected)
that may appear to the client as a single service attachment point.
Keeping the Tunnel_ID consistent across working and protection LSPs
is a useful construct currently employed within GMPLS. However, the
Tunnel_ID for a protection LSP MAY differ from that used by its
corresponding working LSP.
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Internet-Draft MPLS-TP Identifiers June 20115.1. MPLS-TP Point to Point Tunnel Identifiers
At each endpoint a tunnel is uniquely identified by the endpoint's
Node_ID and a locally assigned tunnel number. Specifically a
Tunnel_Num is a 16-bit unsigned integer unique within the context of
the Node_ID. The motivation for each endpoint having its own tunnel
number is to allow a compact form for the MEP-ID. See Section 7.2.1.
Having two tunnel numbers also serves to simplify other signaling
(e.g., setup of associated bidirectional tunnels as described in
Section 5.3).
The concatenation of the two endpoint identifiers serves as the full
identifier. Using the A1/Z9 convention the format of a Tunnel_ID is:
A1-{Node_ID::Tunnel_Num}::Z9-{Node_ID::Tunnel_Num}
Where the Tunnel_ID needs to be globally unique, this is accomplished
by using globally unique Node_IDs as defined above. Thus a globally
unique Tunnel_ID becomes:
A1-{Global_ID::Node_ID::Tunnel_Num}::Z9-{Global_Id::Node_ID::
Tunnel_Num}
When an MPLS-TP Tunnel is configured, it MUST be assigned a unique
IF_ID at each endpoint. As usual, the IF_ID is composed of the local
Node_ID concatenated with a 32-bit IF_Num.
5.2. MPLS-TP LSP Identifiers5.2.1. MPLS-TP Co-Routed Bidirectional LSP Identifiers
A co-routed bidirectional LSP can be uniquely identified by a single
LSP number within the scope of an MPLS-TP Tunnel_ID. Specifically an
LSP_Num is a 16-bit unsigned integer unique within the Tunnel_ID.
Thus the format of an MPLS-TP co-routed bidirectional LSP_ID is:
A1-{Node_ID::Tunnel_Num}::Z9-{Node_ID::Tunnel_Num}::LSP_Num
Note that the uniqueness of identifiers does not depend on the A1/Z9
sort ordering. Thus the identifier
Z9-{Node_ID::Tunnel_Num}::A1-{Node_ID::Tunnel_Num}::LSP_Num
is synonymous with the one above.
At the dataplane level, a co-routed bidirectional LSP is composed of
two unidirectional LSPs traversing the same links in opposite
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directions. Since a co-routed bidirectional LSP is provisioned or
signaled as a single entity, a single LSP_Num is used for both
unidirectional LSPs. The unidirectional LSPs can be referenced by
the identifiers:
A1-Node_ID::A1-Tunnel_Num::LSP_Num::Z9-Node_ID and
Z9-Node_ID::Z9-Tunnel_Num::LSP_Num::A1-Node_ID respectively.
Where the LSP_ID needs to be globally unique, this is accomplished by
using globally unique Node_IDs as defined above. Thus a globally
unique LSP_ID becomes:
A1-{Global_ID::Node_ID::Tunnel_Num}::Z9-{Global_Id::
Node_ID::Tunnel_Num}::LSP_Num
5.2.2. MPLS-TP Associated Bidirectional LSP Identifiers
For an associated bidirectional LSP each of the unidirectional LSPs
from A1 to Z9 and Z9 to A1 require LSP_Nums. Each unidirectional LSP
is uniquely identified by a single LSP number within the scope of the
ingress's Tunnel_Num. Specifically an LSP_Num is a 16-bit unsigned
integer unique within the scope of the ingress's Tunnel_Num. Thus the
format of an MPLS-TP associated bidirectional LSP_ID is:
A1-{Node_ID::Tunnel_Num::LSP_Num}::
Z9-{Node_ID::Tunnel_Num::LSP_Num}
At the dataplane level, an associated bidirectional LSP is composed
of two unidirectional LSPs between two nodes in opposite directions.
The unidirectional LSPs may be referenced by the identifiers:
A1-Node_ID::A1-Tunnel_Num::A1-LSP_Num::Z9-Node_ID and
Z9-Node_ID::Z9-Tunnel_Num::Z9-LSP_Num::A1-Node_ID respectively.
Where the LSP_ID needs to be globally unique, this is accomplished by
using globally unique Node_IDs as defined above. Thus a globally
unique LSP_ID becomes:
A1-{Global_ID::Node_ID::Tunnel_Num::LSP_Num}::
Z9-{Global_Id::Node_ID::Tunnel_Num::LSP_Num}
5.3. Mapping to RSVP Signaling
This section is informative and exists to help understand the
structure of the LSP IDs.
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GMPLS [5] is based on RSVP-TE [2]. This section defines the mapping
from an MPLS-TP LSP_ID to RSVP-TE. At this time, RSVP-TE has yet to
be extended to accommodate Global_IDs. Thus a mapping is only made
for the network unique form of the LSP_ID.
GMPLS and RSVP-TE signaling use a 5-tuple to uniquely identify an LSP
within a operator's network. This tuple is composed of a Tunnel
Endpoint Address, Tunnel_ID, Extended Tunnel ID, and Tunnel Sender
Address and (RSVP) LSP_ID.
For a co-routed bidirectional LSP signaled from A1 to Z9, the mapping
to the GMPLS 5-tuple is as follows:
* Tunnel Endpoint Address = Z9-Node_ID
* Tunnel_ID = A1-Tunnel_Num
* Extended Tunnel_ID = A1-Node_ID
* Tunnel Sender Address = A1-Node_ID
* (RSVP) LSP_ID = LSP_Num
An associated bidirectional LSP between two nodes A1 and Z9 consists
of two unidirectional LSPs, one from A1 to Z9 and one from Z9 to A1.
In situations where a mapping to the RSVP-TE 5-tuples is required,
the following mappings are used. For the A1 to Z9 LSP the mapping
would be:
* Tunnel Endpoint Address = Z9-Node_ID
* Tunnel_ID = A1-Tunnel_Num
* Extended Tunnel_ID = A1-Node_ID
* Tunnel Sender Address = A1-Node_ID
* (RSVP) LSP_ID = A1-LSP_Num
Likewise, the Z9 to A1 LSP, the mapping would be:
* Tunnel Endpoint Address = A1-Node_ID
* Tunnel_ID = Z9-Tunnel_Num
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* Extended Tunnel_ID = Z9-Node_ID
* Tunnel Sender Address = Z9-Node_ID
* (RSVP) LSP_ID = Z9-LSP_Num
6. Pseudowire Path Identifiers
Pseudowire signaling (RFC 4447 [6]) defines two FECs used to signal
pseudowires. Of these, FEC Type 129 along with AII Type 2 as defined
in RFC 5003 [3] fits the identification requirements of MPLS-TP.
In an MPLS-TP environment, a PW is identified by a set of identifiers
which can be mapped directly to the elements required by FEC 129 and
AII Type 2. To distinguish this identifier from other Pseudowire
Identifiers, we call this a Pseudowire Path Identifier (PW_Path_ID).
The AII Type 2 is composed of three fields. These are the Global_ID,
the Prefix, and the AC_ID. The Global_ID used in this document is
identical to the Global_ID defined in RFC 5003. The Node_ID is used
as the Prefix. The AC_ID is as defined in RFC 5003.
To complete the FEC 129, all that is required is an Attachment Group
Identifier (AGI). That field is exactly as specified in RFC 4447. A
(bidirectional) pseudowire consists of a pair of unidirectional LSPs,
one in each direction. Thus for signaling, FEC 129 has a notion of
Source AII (SAII) and Target AII (TAII). These terms are used
relative to the direction of the LSP.
In a purely configured environment when referring to the entire PW,
this distinction is not critical. That is a FEC 129 of AGIa::AIIb::
AIIc is equivalent to AGIa::AIIc::AIIb.
We note that in a signaled environment, the required convention in
RFC 4447 is that at a particular endpoint, the AII associated with
that endpoint comes first. The complete PW_Path_ID is:
AGI::A1-{Global_ID::Node_ID::AC_ID}::
Z9-{Global_ID::Node_ID::AC_ID}.
In a signaled environment the LSP from A1 to Z9 would be initiated
with a label request from A1 to Z9 with the fields of the FEC 129
completed as follows:
AGI = AGI
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SAAI = A1-{Global_ID::Node_ID::AC_ID}
TAII = Z9-{Global_ID::Node_ID::AC_ID}
The LSP from Z9 to A1 would signaled with:
AGI = AGI
SAAI = Z9-{Global_ID::Node_ID::AC_ID}
TAII = A1-{Global_ID::Node_ID::AC_ID}
7. Maintenance Identifiers
In MPLS-TP a Maintenance Entity Group (MEG) represents an Entity that
requires management and defines a relationship between a set of
maintenance points. A maintenance point is either a Maintenance
Entity Group End-point (MEP) or a Maintenance Entity Group
Intermediate Point (MIP). Maintenance points are uniquely associated
with a MEG. Within the context of a MEG, MEPs and MIPs must be
uniquely identified. This section defines a means of uniquely
identifying Maintenance Entity Groups, Maintenance Entities and
uniquely defining MEPs and MIPs within the context of a Maintenance
Entity Group.
7.1. Maintenance Entity Group Identifiers
Maintenance Entity Group Identifiers (MEG_IDs) are required for
MPLS-TP sections, LSPs and Pseudowires. The formats were chosen to
follow the IP compatible identifiers defined above.
7.1.1. MPLS-TP Section MEG_IDs
IP compatible MEG_IDs for MPLS-TP sections are formed by
concatenating the two IF_IDs of the corresponding section using the
A1/Z9 ordering. For example:
A1-IF_ID::Z9-IF_ID
Where the Section_MEG_ID needs to be globally unique, this is
accomplished by using globally unique Node_IDs as defined above.
Thus a globally unique Section_MEG_ID becomes:
A1-{Global_ID::IF_ID}::Z9-{Global_ID::IF_ID}
7.1.2. MPLS-TP LSP MEG_IDs
A MEG pertains to a unique MPLS-TP LSP. IP compatible MEG_IDs for
MPLS-TP LSPs are simply the corresponding LSP_IDs, however, the the
A1/Z9 ordering MUST be used. For bidirectional co-routed LSPs the
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format of the LSP_ID is found in Section 5.2.1. For associated
bidirectional LSPs the format is in Section 5.2.2.
We note that while the two identifiers are syntactically identical,
they have different semantics. This semantic difference needs to be
made clear. For instance if both a MPLS-TP LSP_ID and MPLS-TP LSP
MEG_IDs are to be encoded in TLVs, different types need to be
assigned for these two identifiers.
7.1.3. Pseudowire MEG_IDs
For Pseudowires a MEG pertains to a single PW. The IP compatible
MEG_ID for a PW is simply the corresponding PW_Path_ID, however, the
the A1/Z9 ordering MUST be used. The PW_Path_ID is described in
Section 6. We note that while the two identifiers are syntactically
identical, they have different semantics. This semantic difference
needs to be made clear. For instance if both a PW_Path_ID and a
PW_MEG_ID are to be encoded in TLVs, different types need to be
assigned for these two identifiers.
7.2. MEP_IDs7.2.1. MPLS-TP LSP_MEP_ID
In order to automatically generate MEP_IDs for MPLS-TP LSPs, we use
the elements of identification that are unique to an endpoint. This
ensures that MEP_IDs are unique for all LSPs within a operator. When
Tunnels or LSPs cross operator boundaries, these are made unique by
pre-pending them with the operator's Global_ID.
The MPLS-TP LSP_MEP_ID is
Node_ID::Tunnel_Num::LSP_Num
where the Node_ID is the node in which the MEP is located and
Tunnel_Num is the tunnel number unique to that node. In the case of
co-routed bidirectional LSPs, the single LSP_Num is used at both
ends. In the case of associated bidirectional LSPs, the LSP_Num is
the one unique to where the MEP resides.
In situations where global uniqueness is required this becomes:
Global_ID::Node_ID::Tunnel_Num::LSP_Num
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Internet-Draft MPLS-TP Identifiers June 20117.2.2. MEP_IDs for Pseudowires
Like MPLS-TP LSPs, Pseudowire endpoints (T-PEs) require MEP_IDs. In
order to automatically generate MEP_IDs for PWs, we simply use the
AGI plus the AII associated with that end of the PW. Thus a MEP_ID
used in end-to-end for a Pseudowire T-PE takes the form
AGI::Global_ID::Node_ID::AC_ID
where the Node_ID is the node in which the MEP is located and the
AC_ID is the AC_ID of the Pseudowire at that node.
7.3. Pseudowire Segment Endpoint IDs
In some OAM communications, messages are originated by the node at
one end of a PW segment and relayed to the other end of that same
segment by setting the TTL of the PW label to one (1). For a multi-
segment pseudowire, TTL could be set to any value that would cause
OAM messages to reach the target segment end-point (up to and
including 255). In such communications an identifier for the
pseudowire segment endpoint is needed. We call this a Pseudowire
Segments Endpoint ID or PW_SE_ID.
The PW_SE_ID is formed by a combination of a PW MEP_ID and the
identification of the local node. At an S-PE, there are two PW
segments. We distinguish the segments by using the MEP_ID which is
upstream of the PW segment in question. To complete the
identification we suffix this with the identification of the local
node.
+-------+ +-------+ +-------+ +-------+
| | | | | | | |
| A|---------|B C|---------|D E|---------|F |
| | | | | | | |
+-------+ +-------+ +-------+ +-------+
(T)PE1 (S)PE2 (S)PE3 (T)PE4
Pseudowire Maintenance Points
For example, suppose that in the above figure all of the nodes have
Global_ID GID1; the node are represented as named in the figure; and
The identification for the Pseudowire is:
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AGI = AGI1
A1-Global_ID = GID1
A1-Node_ID = PE1
A1-AC_ID = AII1
Z9-Global_ID = GID1
Z9-Node_ID = PE4
Z9-AC_ID = AII4
The MEP_ID at point A would be -
AGI1::GID1::PE1::AII1
The PW_SE_ID at point B would be -
AGI1::GID1::PE4::AII4::GID1::PE2
The PW_SE_ID at point C would be -
AGI1::GID1::PE1::AII1::GID1::PE2
7.4. MIP Identifiers
At a cross-connect point, in order to automatically generate MIP_IDs
for MPLS-TP, we simply use the IF_IDs of the two interfaces which are
cross-connected via the label bindings of the MPLS-TP LSP or PW.
This allows, two MIPs to be independently identified in one node
where a per-interface MIP model is used. If only a per node MIP
model is used then one MIP is configured. In this case the MIP_ID is
formed using the Node_ID and an IF_Num of 0.
8. IANA Considerations
There are no IANA actions resulting from this document.
9. Security Considerations
This document describes an information model and, as such, does not
introduce security concerns. Protocol specifications that describe
use of this information model, however, may introduce security risks
and concerns about authentication of participants. For this reason,
the writers of protocol specifications for the purpose of describing
implementation of this information model need to describe security
and authentication concerns that may be raised by the particular
mechanisms defined and how those concerns may be addressed.
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